Sky watchers Friday night can get a look at a blue moon, although it will actually look like any other full moon.
The term blue moon applies to the second full moon in a given month, an event that occurs periodically.
The lunar cycle is 29.5 days long, producing full moons typically once a month.
The last blue moon was on Dec. 31, 2009. The next one won’t occur until 2015.
Over a 19-year period, there are seven years with 13 full moons, according to the EarthSky website.
Originally, “blue moon” was applied to the passage of four full moons during a calendar season.